US8571567B2 - Communication terminal device, base station device and radio communication system in which a random access channel is accessed by employing an initial access code randomly selected from a selected group of initial access codes - Google Patents

Abstract

There is disclosed a communication terminal device capable of eliminating collision of access request signals simultaneously transmitted from communication terminal devices in a local cell, preventing generation of interference signal in another cell adjacent to the local cell, and improving the throughput in the local cell. There is also disclosed a base station device for controlling the transmission power of the access permission signal so as to prevent generation of an interference signal in another cell adjacent to the local cell. In this device, a use sub-channel selection unit (206) has a correspondence table between the reception quality of the pilot signals divided into classes and the sub-channel allocated to the classes. According to the correspondence table, the use sub-channel selection unit (206) selects a sub-channel group of RACH correlated to the measurement result of the reception quality of the pilot signals reported from the reception quality measurement unit (205). One sub-channel to be used for transmission of the access request signal is selected at random from the sub-channel group selected.

Description

TECHNICAL FIELD

The present invention relates to a radio communication system, and a communication terminal apparatus and base station apparatus constituting the system.

BACKGROUND ART

Conventionally, in a radio communication system, when a communication terminal apparatus such as a cellular telephone or the like starts radio communication, the communication terminal apparatus receives a pilot signal periodically transmitted from a base station apparatus, and transmits an access request signal subjected open-loop transmission power control (OL-TPC) based on reception quality of the pilot signal to the base station apparatus using a random access channel (RACH). Then, when receiving the access request signal, the base station apparatus transmits an access permission signal to the communication terminal apparatus.

FIG. 1 schematically illustrates a configuration of a conventional radio communication system. The radio communication system as shown inFIG. 1 is comprised ofbase station apparatus11 and a plurality of communication terminal apparatuses12. Further, among the plurality of communication terminal apparatuses12, communication terminal apparatus12-1 is assumed to be positioned nearbase station apparatus11 and in a good reception state. Meanwhile, communication terminal apparatus12-2 is assumed to be positioned near a boundary of a communication area bybase station apparatus11, namely near a cell edge.

FIG. 2 illustrates radio signals on the time series transmitted and received between communication terminal apparatus12 andbase station apparatus11 when communication terminal apparatus12 starts radio communication. As shown inFIG. 2, first,base station apparatus11 transmits a pilot signal with certain power to a plurality of communication terminal apparatuses12 using a common pilot channel (CPICH) on downlink.

Next, when receiving the pilot signal, communication terminal apparatus12 transmits an access request signal with transmission power associated with the reception quality (reception power of the pilot signal on the CPICH inFIG. 2) tobase station apparatus11 using a random access channel (RACH) on uplink. Resources used as a sub-channel of the RACH are predetermined such as, for example, timing, channelization code, subcarrier and the like, and communication terminal apparatus12 randomly selects one from the predetermined resources in transmitting the access request signal.

Subsequently, when receiving the access request signal,base station apparatus11 transmits an access permission signal with certain power to communication terminal apparatus12 using a forward access channel (FACH). Then, when receiving the access permission signal, communication terminal apparatus12 transmits a data packet with transmission power associated with the reception quality of the pilot signal tobase station apparatus11 using a data channel on uplink. In addition, inFIG. 2, the down arrow represents downlink, while the up arrow represents uplink, in each channel.

Further, as well as the conventional technique as described above, a technique is developed that communication terminal apparatus12 first transmits a short packet called preamble tobase station apparatus11 while increasing the transmission power gradually, and whenbase station apparatus11 detects the preamble, communication terminal apparatus12 transmits an access request signal to base station apparatus11 (for example, see Patent Document 1).

• Patent Document 1: Japanese Patent Application Laid-Open No. 2002-528997

DISCLOSURE OF INVENTIONProblems to be Solved by the Invention

However, in the conventional technique as shown inFIG. 2, a plurality of communication terminal apparatuses12 concurrently receives the pilot signal on the CPICH, and randomly selects sub-channels of the RACH to transmit access request signals, so that there is a risk that a plurality of communication terminal apparatuses12 transmits access request signals on the same sub-channel, andbase station apparatus11 cannot receive the access request signals.

Whenbase station apparatus11 cannot receive an access request signal from communication terminal apparatus12,base station apparatus11 does not transmit an access permission signal to communication terminal apparatus12. Therefore, communication terminal apparatus12 determines that the previously transmitted access request signal is not received atbase station apparatus11 after a predetermined time has elapsed since transmission of the access request signal, and transmits the access request signal again tobase station apparatus11 after a lapse of predetermined back-off time. In other words, in such a conventional technique, there is the risk that access request signals transmitted from a plurality of communication terminal apparatuses12 using the RACH are not received atbase station apparatus11 due to collision, the time is required at communication terminal apparatus12 to determine whether the previously transmitted access request signal is received atbase station apparatus11, the predetermined back-off time is further set before communication terminal apparatus12 retransmits the access request signal, and a problem arises that the time increases which is required at communication terminal apparatus12 to start radio communication, and that throughput degrades in the radio communication system.

Further, in the conventional technique, communication terminal apparatus12-2 positioned near the cell edge transmits the access request signal with high power over a plurality of times, so that a problem arises that the access request signal becomes an interfering signal in adjacent other cells.

Furthermore, in the conventional technique, when receiving an access request signal,base station apparatus11 cannot confirm the position of communication terminal apparatus12 transmitting the access request signal, andbase station apparatus11 transmits an access permission signal with a large amount of power to be transmitted using the FACH without performing transmission power control so that all communication terminal apparatuses12 located in the cell can receive the access permission signal, and a problem thereby arises that the access permission signal becomes an interfering signal in adjacent other cells in the same way as described above.

In the technique as disclosed inPatent Document 1, communication terminal apparatus12 transmits the access request signal with required sufficient power obtained by using the preamble tobase station apparatus11, so that the problem is thus improved that the access request signal transmitted from communication terminal apparatus12-2 located near the cell edge becomes an interfering signal in adjacent other cells. However, any improvements are not obtained in the problem that the throughput deteriorates due to the occurrence of collision of the access request signals, and in the problem that the access permission signal transmitted frombase station apparatus11 becomes an interfering signal in adjacent other cells.

It is therefore an object of the invention to provide a communication terminal apparatus which avoids collision of access request signals even when the access request signals are transmitted concurrently from a plurality of communication terminal apparatuses in a cell of the apparatus, prevents the occurrence of an interfering signal in other cells adjacent to the cell, and improves throughput in the cell, and a base station apparatus which controls transmission power of an access permission signal, and prevents the occurrence of an interfering signal in other cells adjacent to a cell of the base station apparatus.

Means for Solving the Problem

A communication terminal apparatus according to the present invention is a communication terminal apparatus which performs radio communication with a base station apparatus, and adopts a configuration provided with a receiving section that receives a pilot signal transmitted from the base station apparatus, a measuring section that measures reception quality of the received pilot signal, a selecting section that selects a sub-channel to be used in transmitting a signal to the base station apparatus according to a measurement result of the reception quality of the pilot signal, and a transmitting section that transmits the signal to the base station apparatus using the selected sub-channel.

Advantageous Effect of the Invention

According to the invention, even when access request signals are transmitted concurrently from a plurality of communication terminal apparatuses in a cell of the apparatuses, it is possible to avoid collision of the signals, prevent the occurrence of an interfering signal in other cells adjacent to the cell, improve throughput in the cell, and further prevent the occurrence of an interfering signal in other cells adjacent to the cell by controlling transmission power of an access permission signal.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram schematically illustrating a configuration of a radio communication system according to conventional technique;

FIG. 2 is a diagram illustrating radio signals on the time series transmitted and received between a communication terminal apparatus and base station apparatus when the communication terminal apparatus starts communication according to the conventional technique;

FIG. 3 is a diagram schematically illustrating a configuration of a radio communication system according toEmbodiment 1 of the present invention;

FIG. 4 is a block diagram illustrating a configuration of a communication terminal apparatus according toEmbodiment 1 of the present invention;

FIG. 5 is a block diagram illustrating a configuration of a base station apparatus according toEmbodiment 1 of the present invention;

FIG. 6 is a diagram illustrating an example of an assignment mode of sub-channels of RACH to each group divided by reception quality of a pilot signal when channelization codes are used as the sub-channels of the RACH inEmbodiment 1 of the present invention;

FIG. 7 is a diagram illustrating another example of the assignment mode of sub-channels of RACH to each group divided by reception quality of the pilot signal when subcarriers in a multicarrier signal are used as the sub-channels of the RACH inEmbodiment 1 of the present invention;

FIG. 8 is a diagram illustrating still another example of the assignment mode of sub-channels of RACH to each group divided by reception quality of the pilot signal when symbols of an OFDM signal are used as the sub-channels of the RACH inEmbodiment 1 of the present invention;

FIG. 9 is a diagram illustrating a correspondence between each group of divided communication terminal apparatuses and reception quality of the pilot signal inEmbodiment 1 of the present invention;

FIG. 10 is a diagram illustrating a correspondence between each group of divided communication terminal apparatuses and transmission power of an access permission signal inEmbodiment 1 of the present invention;

FIG. 11 is a diagram illustrating radio signals on the time series transmitted and received between the communication terminal apparatus and base station apparatus when the communication terminal apparatus starts communication inEmbodiment 1 of the present invention;

FIG. 12 is another diagram illustrating radio signals on the time series transmitted and received between the communication terminal apparatus and base station apparatus when the communication terminal apparatus starts communication inEmbodiment 1 of the present invention;

FIG. 13 is still another diagram illustrating radio signals on the time series transmitted and received between the communication terminal apparatus and base station apparatus when the communication terminal apparatus starts communication inEmbodiment 1 of the present invention;

FIG. 14 is a block diagram illustrating a configuration of a base station apparatus according toEmbodiment 2 of the present invention; and

FIG. 15 is a diagram illustrating a correspondence between each group of divided communication terminal apparatuses and a set of a modulation scheme and coding rate inEmbodiment 2 of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the invention will now be described below in detail with reference to accompanying drawings as appropriate. In addition, in the embodiments, components with the same function are assigned the same reference numerals, and descriptions thereof will be omitted.

(Embodiment 1)

FIG. 3 schematically illustrates a configuration of a radio communication system according toEmbodiment 1 of the present invention. The radio communication system according to this embodiment is comprised of a plurality ofcommunication terminal apparatuses200 andbase station apparatus300. In the radio communication system, the plurality ofcommunication terminal apparatuses200 is classified into three groups based on reception quality of a pilot signal transmitted frombase station apparatus300 on CPICH, for example. Hereinafter, the groups are referred to asgroup1,group2 andgroup3, in descending order of the reception quality. Further, communication terminal apparatuses belonging togroup1 are described as communication terminal apparatuses200-1, communication terminal apparatuses belonging togroup2 are described as communication terminal apparatuses200-2, and communication terminal apparatuses belonging togroup3 are described as communication terminal apparatuses200-3. Accordingly,communication terminal apparatuses200 existing near a cell edge belong togroup3 in the radio communication system.

FIG. 4 is a block diagram illustrating a configuration ofcommunication terminal apparatus200 according toEmbodiment 1 of the invention.Communication terminal apparatus200 hasreception radio section201,channel dividing section202,demodulation section203,decoding section204, receptionquality measuring section205, usedsub-channel selecting section206,coding section207,modulation section208,sub-channel assigning section209, transmissionpower control section211,transmission radio section212 andantenna element213.

Reception radio section201 receives a pilot signal transmitted on CPICH viaantenna element213, access permission signal transmitted on FACH and the like frombase station apparatus300 described later, performs predetermined reception processing such as frequency conversion, analog/digital conversion and the like on the received signals, and inputs the received signals subjected to the reception processing tochannel dividing section202.

Channel dividingsection202 determines a channel used in the received signals input fromreception radio section201, and when the determined channel is the CPICH, inputs the received signal, namely pilot signal to receptionquality measuring section205. Meanwhile, when the determined channel is other than the CPICH namely FACH and the like,channel dividing section202 inputs the received signal todemodulation section203.

Demodulation section203 demodulates the received signal input fromchannel dividing section202 with a predetermined scheme, and inputs the demodulated received signal to decodingsection204.

Decodingsection204 decodes the received signal input fromdemodulation section203 with a predetermined scheme to generate reception data, and inputs the generated reception data to a control section and the like not shown.

Receptionquality measuring section205 measures reception quality of the pilot signal input fromchannel dividing section202, for example, Signal-to-Interference power Ratio (SIR), or a reception power level, and reports the measurement result to usedsub-channel selecting section206 and transmissionpower control section211.

Usedsub-channel selecting section206 has a “correspondence table” between classified reception quality of the pilot signal and sub-channel assigned to each class. Then, based on the correspondence table, usedsub-channel selecting section206 selects a sub-channel group of the RACH associated with the measurement result of the reception quality of the pilot signal reported from receptionquality measuring section205, and randomly selects a single sub-channel for use in transmission of an access request signal from among the selected sub-channel group. Usedsub-channel selecting section206 reports the selected sub-channel to sub-channel assigningsection209. In addition, the correspondence table will be described later where the classified reception quality of the pilot signal and sub-channel of the RACH assigned to each class are indicated.

Coding section207 codes transmission data input from the control section and the like not shown with a predetermined scheme to generate a transmission signal, and inputs the generated transmission signal tomodulation section208.

Modulation section208 modulates the transmission signal input fromcoding section207 with a predetermined scheme, and inputs the modulated transmission signal to sub-channel assigningsection209.

In starting radio communication,sub-channel assigning section209 assigns a predetermined resource to an access request signal input from the control section and the like not shown so as to transmit the access request signal on the sub-channel of the RACH reported from usedsub-channel selecting section206. Examples of the predetermined resource include timing, channelization codes, subcarriers in a multicarrier signal and the like. Then,sub-channel assigning section209 inputs the access request signal assigned the predetermined resource to transmissionpower control section211 at predetermined timing. Further, when an access permission signal is not transmitted frombase station apparatus300 within a predetermined time after inputting the access request signal to transmissionpower control section211,sub-channel assigning section209 assigns again the sub-channel of the RACH reported from usedsub-channel selecting section206 to the access request signal after a lapse of predetermined back-off time, and inputs the assigned access request signal to transmissionpower control section211. Meanwhile, when an access permission signal is transmitted frombase station apparatus300 within a predetermined time after inputting the access request signal to transmissionpower control section211,sub-channel assigning section209 assigns a predetermined resource to the transmission signal input frommodulation section208 so as to transmit the transmission signal on a data channel designated by the access permission signal, and inputs the transmission signal to transmissionpower control section211 at predetermined timing.

Transmissionpower control section211 amplifies the access request signal or transmission signal input from sub-channel assigningsection209 to provide power associated with the measurement result of the reception quality of the pilot signal reported from receptionquality measuring section205, and inputs the amplified access request signal or transmission signal totransmission radio section212.

Transmission radio section212 performs predetermined transmission processing such as digital/analog conversion, frequency conversion and the like on the access request signal or transmission signal input from transmissionpower control section211, and wirelessly transmits the signal tobase station apparatus300 viaantenna element213.

FIG. 5 is a block diagram illustrating a configuration ofbase station apparatus300 according toEmbodiment 1 of the invention.Base station apparatus300 hasreception radio section301,RACH detecting section302,demodulation section303, decodingsection304, required transmissionpower calculating section305,coding section306,modulation section307, transmissionpower control section308, multiplexingsection309,transmission radio section311 andantenna element312.

Reception radio section301 receives the access request signal transmitted on the RACH and transmission signal transmitted on the data channel fromcommunication terminal apparatus200 viaantenna element312, performs predetermined reception processing such as frequency conversion, analog/digital conversion and the like on the received signals, and inputs the received signals subjected to the reception processing toRACH detecting section302.

RACH detecting section302 detects the access request signal from the received signals input fromreception radio section301, and when the access request signal is detected, inputs the access request signal to required transmissionpower calculating section305. Meanwhile, when the access request signal is not detected,RACH detecting section302 determines that the received signals include only normal data signals, and inputs the received signals todemodulation section303.

Demodulation section303 performs demodulation processing on the received signal input fromRACH detecting section302 with a predetermined scheme, and inputs the demodulated received signal todecoding section304.

Decodingsection304 decodes the received signal input fromdemodulation section303 with a predetermined scheme to generate reception data, and inputs the generated reception data to a control section and the like not shown.

Required transmissionpower calculating section305 determines the sub-channel of the RACH used in transmission of the access request signal input fromRACH detecting section302. Required transmissionpower calculating section305 has the correspondence table that used sub-channel selectingsection206 has, and based on the correspondence table, required transmissionpower calculating section305 recognizes the reception quality of the pilot signal incommunication terminal apparatus200 from the determined RACH sub-channel. Further, required transmissionpower calculating section305 also has a “conversion table” that associates the determined sub-channel with transmission power of the access permission signal, calculates the transmission power associated with the determined RACH sub-channel using the conversion table, and reports the calculated transmission power to transmissionpower control section308. In addition, the conversion table will be described later.

Coding section306 performs coding processing on the access permission signal or transmission data input from the control section and the like not shown with a predetermined scheme to generate a transmission signal, and inputs the generated transmission signal tomodulation section307.

Modulation section307 modulates the transmission signal input fromcoding section306 with a predetermined scheme, and inputs the modulated transmission signal to transmissionpower control section308.

Transmissionpower control section308 amplifies the transmission signal input frommodulation section307 to provide power reported from required transmissionpower calculating section305, and inputs the amplified transmission signal to multiplexingsection309.

Multiplexingsection309 receives a pilot signal from the control section and the like not shown periodically, multiplexes the pilot signal on the transmission signal input from transmissionpower control section308 at timing at which the pilot signal is input, and inputs the multiplexed transmission signal totransmission radio section311. In addition, multiplexingsection309 causes the transmission signal input from transmissionpower control section308 to pass throughtransmission radio section311 without change at timing at which the pilot signal is not input.

Transmission radio section311 performs transmission processing such as digital/analog conversion, frequency conversion and the like on the transmission signal input from multiplexingsection309, and wirelessly transmits the transmission signal subjected to the transmission processing tocommunication terminal apparatus200 viaantenna element312.

The operation ofcommunication terminal apparatus200 andbase station apparatus300 will be described below in detail with reference toFIG. 6 toFIG. 13.

FIG. 6 shows an assignment mode of channelization codes togroup1,group2 andgroup3 classified based on the reception quality of the pilot signal whencommunication terminal apparatus200 uses the channelization code as a resource of the sub-channel of the RACH. InFIG. 6, twochannelization codes #1 and #2 are assigned togroup1 with the highest reception quality of the pilot signal, threechannelization codes #3, #4 and #5 are assigned togroup2 with the middle reception quality, and all of remaining usablechannelization codes #6 to #n (n is a natural number of ten or more), are assigned togroup3 with the lowest reception quality.

Further,FIG. 7 shows an assignment mode of subcarriers togroup1,group2 andgroup3 classified based on the reception quality of the pilot signal whencommunication terminal apparatus200 uses the subcarriers in a multicarrier signal as a resource of the sub-channel of the RACH. InFIG. 7, twosubcarriers #1 and #2 are assigned togroup1 with the highest reception quality of the pilot signal, threesubcarriers #3, #4 and #5 are assigned togroup2 with the middle reception quality, and all of remainingusable subcarriers #6 to #n (n is a natural number of ten or more) are assigned togroup3 with the lowest reception quality.

Furthermore,FIG. 8 shows an assignment mode of symbols of an OFDM (Orthogonal Frequency Division Multiplexing) signal togroup1,group2 andgroup3 classified based on the reception quality of the pilot signal whencommunication terminal apparatus200 uses the symbols in an OFDM signal as a resource of the sub-channel of the RACH. InFIG. 8, first two symbols of an OFDM signal are assigned togroup1 with the highest reception quality of the pilot signal, subsequent three symbols of the OFDM signal are assigned togroup2 with the middle reception quality, and all of remaining usable symbols of the OFDM signal are assigned togroup3 with the lowest reception quality. In addition, also when the resource of the sub-channel of the RACH is a time slot standardized in a communication scheme, the time slot can be assigned as in the symbol of an OFDM signal.

FIG. 9 shows an example of the correspondence table provided in usedsub-channel selecting section206. In the correspondence table,group1 is of the case that the measurement result of reception SIR is 15 dB or more as the reception quality of the pilot signal by receptionquality measuring section205,group2 is of the case that the measurement result is 5 to 15 dB, andgroup3 is of the case that the measurement result is −3 to 5 dB.Group1,group2 andgroup3 as shown inFIG. 9 are respectively assigned sub-channels in modes as shown inFIG. 6 toFIG. 8. Accordingly, based on the correspondence table, usedsub-channel selecting section206 selects sub-channels of the RACH assigned in the modes as shown inFIGS. 6 to 8 corresponding to the measurement result of the reception quality of the pilot signal reported from receptionquality measuring section205, and randomly selects one sub-channel to be used in transmitting the access request signal from among the selected plurality of sub-channels. In addition, any groups are not associated with the case that the measurement result is less than −3 dB in the reception quality of the pilot signal by receptionquality measuring section205. This is because when the measurement result of the reception quality of the pilot signal is less than −3 dB, the propagation path condition is excessively poor, and the risk is thereby high thatbase station apparatus300 does not receive an access request signal even whencommunication terminal apparatus200 transmits the access request signal. Therefore, in order to prevent the occurrence of an interfering signal in adjacent other cells,communication terminal apparatus200 is prevented from transmitting an unnecessary access request signal. In addition, in this case, whencommunication terminal apparatus200 recovers from the attenuation due to fading, shadowing or the like on the propagation path and has the measurement result of −3 dB or more in the reception quality of the pilot signal,communication terminal apparatus200 can accessbase station apparatus300.

FIG. 10 shows an example of the conversion table that required transmissionpower calculating section305 has. The conversion table has a correlation with the correspondence table as shown inFIG. 9. On the assumption that the required reception SIR is 0 dB for the access permission signal incommunication terminal apparatus200, the transmission power of the access permission signal inbase station apparatus300 is expressed by decibel based on the transmission power of the pilot signal. More specifically, forgroup1, since the measurement result is 15 dB or more in the reception quality of the pilot signal in communication terminal200-1, in order that the reception quality is 0 dB or more in the access permission signal in communication terminal apparatus200-1, the transmission power of the access permission signal inbase station apparatus300 is set at −15 dB based on the transmission power of the pilot signal. Similarly, forgroup2, since the measurement result is 5 dB or more in the reception quality of the pilot signal in communication terminal200-2, the transmission power of the access permission signal inbase station apparatus300 is set at −5 dB based on the transmission power of the pilot signal. Further, forgroup3, since the measurement result is −3 dB or more in the reception quality of the pilot signal in communication terminal200-3, the transmission power of the access permission signal inbase station apparatus300 is set at 3 dB based on the transmission power of the pilot signal.

FIG. 11 illustrates radio signals on the time series transmitted and received between communication terminal apparatus200-1 belonging togroup1 andbase station apparatus300 when communication terminal apparatus200-1 starts communication. Similarly,FIG. 12 illustrates radio signals on the time series transmitted and received between communication terminal apparatus200-2 belonging togroup2 andbase station apparatus300 when communication terminal apparatus200-2 starts communication. Further,FIG. 13 illustrates radio signals on the time series transmitted and received between communication terminal apparatus200-3 belonging togroup3 andbase station apparatus300 when communication terminal apparatus200-3 starts communication. In addition, inFIG. 11 toFIG. 13, a reception power level of a pilot signal is used as the reception quality of the pilot signal. As shown inFIG. 11 toFIG. 13, based on the measurement result of the reception quality of the pilot signal, communication terminal apparatuses200-1 to200-3 perform transmission power control on the access request signal transmitted on the RACH and a data packet transmitted on the data channel. Meanwhile,base station apparatus300 determines the sub-channel of the RACH used bycommunication terminal apparatus200, indirectly recognizes the measurement result of the reception quality of the pilot signal incommunication terminal apparatus200, namely recognizes thatcommunication terminal apparatus200 belongs to which group amonggroups1 to3, and performs transmission power control on the access permission signal transmitted on the FACH. Accordingly, by comparing betweenFIG. 11 andFIG. 13, it is understood that the transmission power on the FACH to transmit the access permission signal is different from one another, and that the transmission power on the FACH is the highest inFIG. 13 showing communication terminal apparatus200-3 with the lowest reception quality of the pilot signal.

Thus, according to the radio communication system according to this Embodiment,communication terminal apparatus200 classifies measurement results of the reception quality of the pilot signal, assigns dedicated RACH sub-channels to each class beforehand, and selects an RACH sub-channel to use in transmitting an access request signal according to an actual measurement result, so that it is possible to decrease the probability that a plurality ofcommunication terminal apparatuses200 concurrently uses the same RACH sub-channel. As a result, according to the radio communication system according to this embodiment, the access request signal is received reliably inbase station apparatus300, the number of retransmissions of the access request signal decreases, so that it is possible forcommunication terminal apparatus200 to start radio communication in a short period, improve throughput in the cell, and prevent the occurrence of an interfering signal in other cells adjacent to the cell.

Further, according to the radio communication system according to this embodiment,base station apparatus300 transmits the access permission signal with required sufficient transmission power according to the reception quality of the access request signal in each of communication terminal apparatuses200-1 to200-3, so that it is possible to prevent the access permission signal from being an interfering signal in other cells adjacent to the cell ofbase station apparatus300.

Furthermore, according to the radio communication system according to this embodiment, in the correspondence table provided in usedsub-channel selecting section206 incommunication terminal apparatus200, a larger number of sub-channels are assigned to a lower class (for example, group3) than a higher class (for example, group1) in classified reception quality of the pilot signal. By this means,communication terminal apparatuses200 positioned nearer the cell edge decrease the probability of concurrently using the same RACH sub-channel, and the number of retransmissions of the access request signal decreases that it is possible to efficiently prevent the occurrence of the interfering signal in other cells adjacent to the cell ofcommunication terminal apparatuses200.

Moreover, in the radio communication system according to this embodiment, in the correspondence table provided in usedsub-channel selecting section206 atcommunication terminal apparatus200, with respect to the classified reception quality of the pilot signal, a range of the reception quality in a lower class is narrower than that in a higher class. More specifically, the range of the reception quality ofgroup1 is 15 dB or more without an upper limit, the range of the reception quality ofgroup2 is 10 dB of between 5 and 15 dB, and the range of the reception quality ofgroup3 is 8 dB of between −3 and 5 dB. Therefore, according to the radio communication system according to this embodiment, since a larger number of sub-channels are assigned to a lower class with a narrower range of the reception quality of the pilot signal, it is possible to further reduce efficiently the number of retransmissions of the access request signal ofcommunication terminal apparatus200 positioned near the cell edge, so that it is possible to prevent the occurrence of the interfering signal in other cells adjacent to the cell ofcommunication terminal apparatus200 more effectively.

In addition, this embodiment may be modified and applied as described below.

Inbase station apparatus300 according to this embodiment, the case has been described where required transmissionpower calculating section305 determines a sub-channel of the RACH used in transmission of the access request signal, and reports transmissionpower control section308 of transmission power associated with the determined sub-channel, but the invention is not limited to this case. For example, required transmissionpower calculating section305 may have a request signal measuring section that measures reception quality of an access request signal, compare the reception quality measured in the request signal measuring section with required reception quality incommunication terminal apparatus200, namely target reception quality in transmission power control, increase or decrease the transmission power associated with the sub-channel of the RACH when a difference of the reception quality is larger than a predetermined value, and report the increased or decreased transmission power to transmissionpower control section308.

Calculation of the transmission power of the access permission signal in required transmissionpower calculating section305 is calculation by closed-loop based on the reception quality of the access request signal Therefore, when the time is required atcommunication terminal apparatus200 from the reception of a pilot signal until the transmission of an access request signal or when the variation is intense in propagation path conditions, there is a risk that actual propagation path conditions are not reflected in the calculated transmission power. Then, if required transmissionpower calculating section305 performs calculation of the transmission power by open-loop for measuring the reception quality of the access request signal, in addition to calculation of the transmission power by closed-loop, it is possible to perform transmission power control of the access permission signal more accurately.

(Embodiment 2)

Embodiment 2 of the invention describes the case where a base station apparatus varies adaptively a coding rate and modulation scheme on the FACH based on used resources of the RACH. In addition, a configuration of a communication terminal apparatus according to this embodiment is the same as that inFIG. 4, and described usingFIG. 4.

FIG. 14 is a block diagram illustrating a configuration ofbase station apparatus400 according toEmbodiment 2 of the invention.Base station apparatus400 hasreception radio section301,RACH detecting section302,demodulation section303, decodingsection304,adaptive control section413,coding section406,modulation section407, multiplexingsection309,transmission radio section311 andantenna element312.

Adaptive control section413 determines a sub-channel of the RACH used in transmission of an access request signal input fromRACH detecting section302, sets a modulation scheme and coding rate using a conversion table that associates the determined sub-channel with a transmission parameter, namely a set of the modulation scheme and coding rate of an access permission signal, and inputs the set modulation scheme and coding rate tocoding section406 andmodulation section407.

Coding section406 performs coding processing on the access permission signal or transmission data input from the control section and the like not shown with the coding rate or coding method according to the transmission parameter (information of the coding rate and modulation scheme) input fromadaptive control section413 to generate a transmission signal, and inputs the generated transmission signal tomodulation section407.

Modulation section407 modulates the transmission signal input fromcoding section406 with the modulation scheme according to the transmission parameter input fromadaptive control section413, and inputs the modulated transmission signal to multiplexingsection309.

FIG. 15 shows an example of the conversion table thatadaptive control section413 has. The conversion table has a correlation with the correspondence table as shown inFIG. 9, and as the reception quality incommunication terminal apparatus200 is higher, the modulation level and coding rate increase. For example, ingroup1, since the reception quality is 15 dB or more, the transmission parameter such that the required SIR is 15 dB, namely 16QAM and R=3/4 is used that is the transmission parameter with the highest transmission efficiency enabling reception with a sufficiently low error rate when the reception SIR is 15 dB or more. Ingroup2, since the reception SIR is 5 dB to 15 dB, QPSK and R=1/2 is used that is the transmission parameter such that the reception SIR is 5 dB. The same also applies togroup3.

As the transmission parameter has higher transmission efficiency, it is possible forbase station apparatus400 to finish transmission of the access permission signal in a shorter time.

Thus, according to this embodiment,base station apparatus400 transmits an access permission signal using a transmission parameter with the highest transmission efficiency that allows reception with a sufficiently low error rate according to the reception quality of the access request signal in each of communication terminal apparatuses200-1 to200-3, so that it is possible to reduce the transmission time of the access permission signal, and prevent the access permission signal from being an interfering signal in other cells.

Each of the above-mentioned Embodiments has described the case where the invention is constructed by hardware as an example, but it is also possible to implement the present invention by software.

Each function block employed in the description of each of the aforementioned embodiments may typically be implemented as an LSI constituted by an integrated circuit. These may be individual chips or partially or totally contained on a single chip. “LSI” is assumed here but this may also be referred to as “IC”, “system LSI”, “super LSI”, “ultra LSI” depending on differing extents of integration.

Further, the method of circuit integration is not limited to LSI's, and implementation using dedicated circuitry or general purpose processors is also possible. After LSI manufacture, utilization of an FPGA (Field Programmable Gate Array) or a reconfigurable processor where connections and setting of circuit cells within an LSI can be reconfigured is also possible.

Furthermore, if integrated circuit technology comes out to replace LSI's as a result of the advancement of semiconductor technology or a derivative other technology, it is naturally also possible to carry out function block integration using this technology. Application in biotechnology is also possible.

In addition, in the radio communication system according to each of the above-mentioned embodiments, the case has been described where a plurality ofcommunication terminal apparatuses200 is divided into three groups in association with classes of the reception quality of the pilot signal, but the invention is not limited to this case. For example, the number of groups may be increased.

Further, the access permission signal may be transmitted, for example, in 3GPP standards, using AICH (Acknowledge Indicator Channel), FACH (Forward Access Channel), S-CCPCH (Secondary-Common Control Physical Channel), HS-SCCH (High Speed-Shared Control Channel), and DPCH (Dedicated Physical Channel).

Furthermore, in each of the above-mentioned embodiments, it is described that an access request is made on the RACH, access permission is made on the FACH, and then, data packets are transmitted. However, the same effects are obtained when the RACH is used in transmission of data as well as the access request signal, and the FACH is used in transmission of data as well as the access permission signal. For example, for a short packet, packet with demanding delay requirement and the like, the data packet on uplink may be transmitted on the RACH, while the data packet on downlink may be transmitted on the FACH.

Still furthermore, the RACH in each of the above-mentioned embodiments may be another comparable channel to which resource are not assigned beforehand for each user.

Moreover, in each of the above-mentioned embodiments, it is described that the reception quality is estimated from the reception SIR, but the reception quality may be estimated from reception SNR, reception CIR, reception SINR, reception CINR, reception power, interfering power, bit error rate, throughput, MCS (a combination of a modulation scheme and coding rate) capable of achieving a predetermined error rate, and the like. Further, the base station apparatus may be represented by Node B, and the communication terminal apparatus may be represented by UE.

A first aspect of the invention is a communication terminal apparatus which performs radio communication with a base station apparatus, and has a receiving section that receives a pilot signal transmitted from the base station apparatus, a measuring section that measures reception quality of the received pilot signal, a selecting section that selects a sub-channel to be used in transmitting a signal to the base station apparatus according to a measurement result of the reception quality of the pilot signal, and a transmitting section that transmits the signal to the base station apparatus using the selected sub-channel.

A second aspect of the invention is a communication terminal apparatus where in the above-mentioned invention, the transmitting section transmits the signal using a random access channel.

A third aspect of the invention is a communication terminal apparatus where in the above-mentioned invention, the transmitting section transmits an access request signal.

A fourth aspect of the invention is a communication terminal apparatus where the selecting section assigns a larger number of sub-channels to a lower class than a higher class in classified reception quality, and selects the sub-channel to be used in transmitting the signal to the base station apparatus from among sub-channels assigned to a class corresponding to the measurement result of the reception quality of the pilot signal.

A fifth aspect of the invention is a communication terminal apparatus where in the above-mentioned invention, the selecting section assigns sub-channels to each class by narrowing a range of the reception quality for a lower class than a higher class in the classified reception quality, and selects the sub-channel to be used in transmitting the signal to the base station apparatus from among the sub-channels assigned to the class corresponding to the measurement result of the reception quality of the pilot signal.

A sixth aspect of the invention is a base station apparatus which performs radio communication with a communication terminal apparatus, and has a receiving section that receives a signal transmitted from the communication terminal apparatus, a detecting section that detects a sub-channel used in transmitting the received signal, and a transmitting section that transmits the signal to the communication terminal apparatus with transmission power associated with the detected sub-channel, or a modulation scheme and coding rate associated with the detected sub-channel.

A seventh aspect of the invention is the base station apparatus where in the above-mentioned invention, the transmitting section transmits an access permission signal.

An eighth aspect of the invention is a base station apparatus where in the above-mentioned embodiment, a request signal measuring section is further provided that measures reception quality of the signal received by the receiving section, and the transmitting section increases or decreases transmission power associated with the sub-channel detected in the detecting section, according to a difference between the reception quality measured by the request signal measuring section and target reception quality in transmission power control, and transmits the signal with increased or decreased power to the communication terminal apparatus.

A ninth aspect of the invention is a base station apparatus where in the above-mentioned invention, the receiving section receives the signal transmitted using a random access channel.

A tenth aspect of the invention is a radio communication system comprised of a communication terminal apparatus and a base station apparatus, where the communication terminal apparatus has a terminal receiving section that receives a pilot signal transmitted from the base station apparatus, a measuring section that measures reception quality of the received pilot signal, a selecting section that selects a sub-channel to be used in transmitting a signal to the base station apparatus according to a measurement result of the reception quality of the pilot signal, and a terminal transmitting section that transmits the signal to the base station apparatus using the selected sub-channel, and the base station apparatus has a base station receiving section that receives the signal transmitted from the communication terminal apparatus, a detecting section that detects the sub-channel used in transmitting the received signal, and a base station transmitting section that transmits the signal to the communication terminal apparatus with transmission power associated with the detected sub-channel.

An eleventh aspect of the invention is a radio communication system where in the above-mentioned invention, the terminal transmitting section transmits an access request signal.

A twelfth aspect of the invention is a radio communication system where in the above-mentioned invention, the base station transmitting section transmits an access permission signal.

The present application is based on Japanese Patent Application No. 2004-173017, filed on Jun. 10, 2004, entire content of which is expressly incorporated by reference herein.

Industrial Applicability

The communication terminal apparatus and base station apparatus according to the present invention have effects of decreasing the incidence of collision of access request signals in a cell of the apparatus, preventing the occurrence of an interfering signal in other cells adjacent to the cell, and improving throughput in the cell, and are useful in a radio communication system and the like.

Claims (18)

The invention claimed is:

1. A radio terminal apparatus using a random access channel (RACH), the apparatus comprising:

a receiving section that receives a pilot signal transmitted from a base station apparatus;

a measuring section that measures a reception power of the pilot signal;

a selecting section that selects, based on the reception power measured by the measuring section, one code group among a plurality of code groups into which codes for contention based initial access before a connection to the base station apparatus is established are divided, the code groups being respectively associated with different ranges of reception powers at the radio terminal apparatus; and

a transmitting section that performs a transmission to the base station apparatus for the contention based initial access via the RACH using a code randomly selected from codes of the selected one code group, whereby the selected one code group to which said code belongs provides an indication to the base station apparatus of radio condition at the radio terminal apparatus,

wherein a range of a lower reception power is narrower than a range of a higher reception power such that a larger number of codes are included in a code group associated with a lower reception power than a code group associated with a higher reception power, and no code group is associated with a reception power that is less than a given value.

2. The radio terminal apparatus according toclaim 1, wherein said transmitting section performs the transmission as an access request.

3. The radio terminal apparatus according toclaim 1, wherein the codes are grouped into the groups at the base station apparatus.

4. A base station apparatus using a random access channel (RACH), the apparatus comprising:

a receiving section that receives data transmitted for contention based initial access from a radio terminal apparatus using a random access channel (RACH), the radio terminal apparatus comprising a receiving section that receives a pilot signal transmitted from the base station apparatus, a measuring section that measures a reception power of the pilot signal, a selecting section that selects, based on the reception power measured by the measuring section, one code group among a plurality of code groups into which codes for contention based initial access before a connection to the base station apparatus is established are divided, the code groups being respectively associated with different ranges of reception powers at the radio terminal apparatus, and a transmitting section that performs a transmission to the base station apparatus for the contention based initial access via the RACH using a code randomly selected from codes of the selected one code group, whereby the selected one code group to which said code belongs provides an indication to the base station apparatus of radio condition at the radio terminal apparatus, wherein a range of a lower reception power is narrower than a range of a higher reception power such that a larger number of codes are included in a code group associated with a lower reception power than a code group associated with a higher reception power, and no code group is associated with a reception power that is less than a given value;

an assigning section that assigns the codes to the groups which are respectively associated with the different reception powers and each of which provides an indication of radio condition at the radio terminal apparatus; and

a transmitting section that transmits data to the radio terminal apparatus based on the code used in the received data.

5. The base station apparatus according toclaim 4, wherein said receiving section receives data as an access request.

6. A base station apparatus using a random access channel (RACH), the apparatus comprising:

a transmitting section that transmits a pilot signal to a radio terminal apparatus; and

a receiving section that receives data transmitted for contention based initial access before a connection of the radio terminal apparatus to the base station apparatus is established from the radio terminal apparatus using a code, which is randomly selected by said radio terminal apparatus from codes of one of groups which is selected based on a reception power of the pilot signal at the radio terminal apparatus, codes being grouped into the groups respectively associated with different ranges of reception powers of the pilot signal, and the selected one group to which the selected code belongs provides an indication to the base station apparatus of radio condition at the terminal apparatus, wherein:

said transmitting section further transmits data to the radio terminal apparatus based on the code used in the data transmitted for the contention based initial access,

wherein a range of a lower reception power is narrower than a range of a higher reception power such that a larger number of codes are included in a code group associated with a lower reception power than a code group associated with a higher reception power, and no code group is associated with a reception power that is less than a given value.

7. The base station apparatus according toclaim 6, wherein said transmitting section transmits data based on the reception power with which the code used in the received data is associated.

8. The base station apparatus according toclaim 7, wherein said transmitting section transmits data with a transmission power associated with the reception power.

9. The base station apparatus according toclaim 6, wherein said receiving section receives data as an access request, and said transmitting section transmits data as an access permission.

10. A radio communication system using a random access channel (RACH) comprising a base station and a terminal, wherein:

said terminal comprises:

a receiving section that receives a pilot signal;

a measuring section that measures a reception power of the pilot signal;

a selecting section that selects, based on the reception power measured by the measuring section, one code group among a plurality of code groups into which codes for contention based initial access before a connection to the base station apparatus is established are divided, the code groups being respectively associated with different ranges of reception powers at the radio terminal apparatus; and

a transmitting section that transmits data for the contention based initial access via the RACH using a code randomly selected from codes of the selected one code group, whereby the selected one code group to which said code belongs provides an indication to the base station apparatus of radio condition at the radio terminal apparatus; and said base station comprises:

a transmitting section that transmits the pilot signal; and

a receiving section that receives from said terminal the data transmitted for the contention based initial access,

wherein a range of a lower reception power is narrower than a range of a higher reception power such that a larger number of codes are included in a code group associated with a lower reception power than a code group associated with a higher reception power, and no code group is associated with a reception power that is less than a given value.

11. The radio communication system according toclaim 10, wherein:

said transmitting section in said terminal transmits data as an access request; and

said transmitting section in said base station transmits data as an access permission.

12. A method for radio communication using a random access channel (RACH), the method comprising:

receiving a pilot signal, which is transmitted from a base station apparatus, at a radio terminal apparatus;

measuring a reception power of the pilot signal;

selecting, based on the reception power, one code group among a plurality of code groups into which codes for contention based initial access before a connection to the base station apparatus is established are divided, the code groups being respectively associated with different ranges of reception powers at the radio terminal apparatus; and

performing a transmission to the base station apparatus for the contention based initial access via the RACH using a code randomly selected from codes of the selected one code group, whereby the selected one code group to which said code belongs provides an indication to the base station apparatus of radio condition at the radio terminal apparatus,

wherein a range of a lower reception power is narrower than a range of a higher reception power such that a larger number of codes are included in a code group associated with a lower reception power than a code group associated with a higher reception power, and no code group is associated with a reception power that is less than a given value.

13. The method for radio communication according toclaim 12, wherein the transmission is performed as an access request.

14. The radio terminal apparatus according toclaim 1, wherein said transmitting section performs the transmission to the base station apparatus for the contention based initial access using the selected code with a transmission power determined based on the reception power measured by the measuring section.

15. The radio terminal apparatus according toclaim 1, wherein said transmitting section performs the transmission as an access request to the base station apparatus for the contention based initial access using the selected code with a transmission power determined based on the reception power measured by the measuring section, said receiving section receives an access grant transmitted from the base station apparatus in response to the access request, and said transmitting section transmits data to the base station apparatus with a transmission power determined based on the reception power measured by the measuring section in response to the access grant.

16. The radio terminal apparatus according toclaim 1, wherein a predetermined number of the codes among available codes are contained in one of the groups, and the rest of the codes are contained in others of the groups.

17. The base station apparatus according toclaim 6, wherein said receiving section receives data transmitted for the contention based initial access using the selected code with a transmission power determined based on the reception power measured at the radio terminal apparatus.

18. The base station apparatus according toclaim 6, wherein said receiving section receives data as an access request for the contention based initial access using the selected code with a transmission power determined based on the reception power measured at the radio terminal apparatus, said transmitting section transmits an access grant to the radio terminal apparatus in response to the access request, and said receiving section receives data transmitted from the radio terminal apparatus with a transmission power determined based on the reception power measured at the radio terminal apparatus in response to the access grant.

Images